This invention relates to the continuous forming of fastener products with elements extending from a base, and has particular application to the production of fastener elements for touch fasteners and the like.
Some fastening elements are capable of engaging fibrous loops to form a fastening, while some are termed "self-engaging" as they are constructed and arranged to releasably engage similar fastener elements. Sometimes the latter are employed on fastening strips that are thereby looped to overlay, and fasten with, themselves.
Some fastening elements are hook-shaped, with distal ends that extend in discrete directions from their stems. Fastening elements with heads that overhang their stems generally equally in all directions are sometimes referred to as "mushroom" fastening elements. Some hook-shaped fastening elements have more than one distal end. Hooks with two oppositely-directed distal ends are sometimes called "palm-tree" hooks.
Hook-shaped fastener elements for touch fasteners and other products are effectively produced by the machine and method of Fischer U.S. Pat. No. 4,794,028, which is hereby incorporated by reference. In commercial production, fastener products are effectively produced in a continuous molding process employing a rotating mold roll. The mold roll has a large number of thin, disk-shaped mold rings and spacer rings which are stacked concentrically about a central barrel. At the periphery of the mold rings are hook-shaped cavities for molding the fastening elements. Molten resin is introduced to the surface of the mold roll and, under pressure, fills the cavities. The outer surface of the mold roll simultaneously forms one side of the strip-form base which, after being trained about the mold roll a sufficient distance and time to permit sufficient cooling of the resin, is stripped from the mold roll surface, pulling the formed fastener elements from their cavities without opening the cavities themselves.
Mushroom-type fastening elements are often produced by weaving a plastic fiber into a sheet form base to form a series of loops, cutting the loops to form stems, and melting the distal ends of the stems. In part because the plastic fiber (e.g., polypropylene) is a drawn fiber with high molecular alignment and residual strain along its axis, the molten resin of the stem ends draws back to form free-form, hemispherical heads overhanging the unmelted lower portions of the stems. Frequently the distal ends of the stems are melted by passing them near a hot wire or heated platen.
Because of their omni-directional overhanging portions, mushroom-type fastening elements are especially suitable for loop-engaging applications requiring shear strength in many different directions.